1. Field of the Invention
The present invention relates to an electric control apparatus for fuel injection pumps, which is so designed that the desired value of the fuel injection quantity is computed electrically and also the net fuel flow through the fuel injection pump is detected by an electric fuel flow sensor, thereby controlling the fuel injection quantity of the fuel injection pump.
2. Description of the Prior Art
A prior art fuel injection quantity control apparatus for fuel injection pumps, which includes an electric computing unit, is so designed that a position of a fuel controlling element which is estimated to provide a predetermined fuel injection quantity corresponding to engine operating conditions is computed as a desired position (signal) and the actual position of the fuel controlling element is also computed as an actual position (signal), so that the error between the actual position signal and the desired position signal is detected to drive an electric servo device, thereby operating the fuel controlling element.
This known apparatus does not directly detect a fuel injection quantity itself which is the primary object of its control, but it employs an indirect fuel injection quantity detecting system in which the position of the fuel controlling element is detected by a position sensor to determine the fuel injection quantity from the detected position. Thus, there is a disadvantage that, no matter how the detection accuracy of the position sensor is improved, the effect of improving the fuel injection quantity detection accuracy is not obtainable because of variations in the fuel injection quantity characteristic at the respective positions of the fuel controlling element such as a fuel control rack, etc. of each fuel injection pump.
Another disadvantage is that, even with respect to the same fuel injection pump, the fuel injection quantity characteristics at the respective positions of the fuel controlling element may vary depending on the pump speeds and hence the engine speeds and besides the variations with time occur as the service time increases, thus making it impossible to determine the actual fuel injection quantity only by the position of the fuel controlling element.